Radiographic imaging, in its simplest expression, is an X-ray beam traversing an object and a detector relating the overall attenuation per ray. The attenuation is derived from a comparison of the same ray with and without the presence of the object. From this conceptual definition, several aspects are required to properly construct an image in 3D. For instance, the finite size of the X-ray focal spot, the nature and shape of the filter blocking the very low-energy X-ray from the tube, the details of the geometry and characteristics of the detector and the capacity of the data acquisition system are all elements that affect how the actual reconstruction is performed.
CdTe/CZT-based photon-counting detectors suffer from polarization upon irradiation by non- or low-attenuated beams near the edges of the scan field of view (FOV) and/or after scanning low-attenuation regions of the patient, e.g., the lung. Dynamic (mechanical) bowtie filters or collimators that attempt to attenuate such beams to compensate for the variations in patient size and shape is not feasible due to fast CT gantry rotation speeds, high centrifugal forces on the gantry rotating base, and system reliability challenges.